Wednesday 5 January 2011 02.00 EST
First published on Wednesday 5 January 2011 02.00 EST

In climate change, a feedback loop is the equivalent of a vicious or virtuous circle – something that accelerates or decelerates a warming trend. A positive feedback accelerates a temperature rise, whereas a negative feedback decelerates it.

Scientists are aware of a number of positive feedbacks loops in the climate system. One example is melting ice. Because ice is light-coloured and reflective, a large proportion of the sunlight that hits it is bounced back to space, which limits the amount of warming it causes. But as the world gets hotter, ice melts, revealing the darker-coloured land or water below. The result is that more of the sun's energy is absorbed, leading to more warming, which in turn leads to more ice melting – and so on.

Various other feedbacks – related to emissions from soils and permafrost, for example, and changes to ocean evaporation – are known or thought to exist.

Feedback loops such as these are complex in themselves and even more complex when considered as part of an integrated global climate system. Some are already at work, while others have yet to kick in. Others still – both positive and negative – may yet be discovered. These uncertainties, coupled with historical evidence for the climate changing rapidly in the past, led one prominent climate scientist to compare releasing greenhouse gases into the air with "poking a beast with a sharp stick".